1. Field of the Invention
This invention relates generally to the field of railroad hot wheel detection and specifically to a hot wheel simulator which verifies proper operation of hot wheel detectors.
2. Description of Related Art
Hot wheel detectors are commonly used on railroads. The detectors include heat sensing scanners which are located at designated points along railroad tracks. The scanners sense the temperature of wheels on passing railroad rolling stock and, typically, transmit the sensed temperature information to a telemetry unit. At the telemetry unit, the sensed wheel temperature is compared against a reference and, if the reference temperature is exceeded, an alarm is transmitted via the telemetry unit to the locomotive engineer or a control tower.
The detectors are usually optical pyrometers aimed at the top of the rail or just above the top of the rail to detect excessive heat. A detector is typically aimed at an acute angle with respect to the tracks, so that it measures the thermal radiation from a wheel on the near rail and then, as the train moves past, from a corresponding wheel on the far rail. The thermal radiation measured is converted to a temperature reading.
Frequently, the detectors are activated by magnetic sensing transducers mounted near the rail which are triggered by the metal of the wheel. The magnetic sensors can be located near the detector location to activate the detector as each wheel passes or the sensors can be located to activate the detector for the entire duration of a train and deactivate the detector after the train has passed.
A hot wheel, as is known in the art, is one which has exceeded a certain temperature, thereby indicating an undesirable condition. A hot wheel can be caused by a number of problems. Most commonly, a wheel which is not rotating properly because of a stuck brake or a hindrance will create excessive friction between the wheel and the rail. A hot wheel which is not detected results in decreased efficiency and possibly greater problems such as derailment. Consequently, it is important that the detectors properly detect hot wheels. When a hot wheel is detected, the train is stopped to determine if the wheel is actually hot. If it is hot, the car is removed from service to be repaired. If the wheel is not hot, the stoppage creates an unnecessary delay. Therefore, it is important that train stoppages for hot wheels occur only when a wheel is actually defective. Thus, all hot wheel detectors must be properly aligned and calibrated to detect heat in the correct location and temperature range.
Verification and maintenance of hot wheel detectors is typically carried out by railroad employees who travel along the track periodically and who stop and verify the detectors along the route. Such maintenance and calibration procedures are labor intensive and expensive. More importantly, maintenance personnel are able to check the detectors only under static conditions. Hot wheel detectors may appear to be operating properly under static conditions but may, in fact, fail to detect hot wheels under the dynamic conditions created by passing trains.
It is desirable to provide an apparatus for verifying hot wheel detectors which monitors the operation of such detectors under dynamic conditions caused by the passage of a load along the railroad track. A heater for simulating a hot wheel could be located outboard of a wheel and be suspended below the truck or it could be mounted on a bracket with a hot bearing simulator. However, the Association of American Railroads has defined a railroad car profile in which a car and all its attachments must fit to maintain safe clearances on American railroads. This simulator must not interfere with the standard clearances and should be protected from impact with objects in the path of the train.
A problem related to hot wheels is hot wheel bearings on railroad rolling stock. Hot bearing detectors are known and are often installed jointly with hot wheel detectors. Dynamic hot bearing simulators have been described, for example, in U.S. Pat. Nos. 4,878,437 and 4,974,797 to Myers et al. These hot bearing simulators direct heat vertically downwardly to trigger the hot bearing sensors which scan generally upwardly. It is desirable to have a hot wheel simulator which can be installed with a hot bearing simulator so that they can operate and cooperate simultaneously.